The present invention relates to a latex composition with improved viscosity stability in paint.
Viscosity drift, more particularly Krebs Unit viscosity drift (KU drift) in paint formulations is undesirable because formulators and final users want to achieve a target viscosity with assurance of stability of that viscosity. Some paint formulations that contain latex polymers that adsorb to the surfaces of pigment particles to form composites are especially prone to KU drift, especially where the rate of adsorption of the adsorbing latex (also known as the pre-composite) and the pigment particles, typically TiO2 particles, is slow. This slow adsorption is attributed to the presence of adsorbing inefficiencies arising from the surface treatment of the TiO2 particles, which slows down the rate of adsorption between the latex particles and the TiO2 particles; additionally, surface active agents used to prepare TiO2 slurries may also adversely affect the rate at which the adsorbing latex particles adsorb to the TiO2 particles. Moreover, associative thickeners such as hydrophobically modified ethylene oxide urethane polymers (HEURs) and hydrophobically modified alkali swellable or soluble emulsions (HASEs), which form a network with the latex particles, are believed to interfere with the ability of these particles to adsorb to the surface of the TiO2 particles.
Therefore, it would be an advance in the art of pigment-adsorbing latex technology to find a way to eliminate or substantially reduce viscosity drift in paint formulations.